Humidification of wood fiber sheets



in 0R 4 Q r HARDBOARD SUB G PRESS y PRES 0 Aug. 20, 1963 o. STEWART 3,101,105

'HUMIDI TION OF WOOD FIBER'SHEETS Filed March 14, 1960 |o l4 UNIFORMLY DENSITY HUMIDIFIED RD DRYER Q SURFACE PRODUCT DRYER E I INVENTO 1 Fig 3 Basil 0. Stew ATTORNEY easily operable equipment subject to complete ease of minute and normal resiliency of the board- The larger undergoing humidification in accordance with the inventhat, due to the Patented Aug. 20, 1963 United States Patent ce WW l 2 3,101,105 3 is a fragmentary side sectional view of a portion of the wood fiber sheet of FIG. 2 showing the re- HUMIDIFICATION 0F WOOD FIBER SHEETS i Basil 0. Stewart, Kenmore, N.Y., assignor to National. eXpa-nswn actlon which provldes (the umformlty of \hu yp p y Buffalo NY a curpomfion of midification by a controlled suction of the surrounding Delaware 5 Water i Ffled 14, 1960,- Ser. 14,851 In the of making wood fiber board products, there 6 Claims (CL 144 327) are primarily two processing steps 1nvolvn1g the increasing of the moisture content of a wood fiber board. After This invention relates to a method of mechanically forming a water laid web of wood fiber into board form, humidifying a substantially bone dry wood fiber sheet to the board is normally dried to substantially bone-dry conbring the moisture content thereof up to the percentage dition. v to which it naturally would tend ,to come undernonmial Unless this dried low density board is to be immediately atmospheric conditions, and particularly a method of proconsolidated into hardboard under high temperature, high viding uniform humidification of a previously oven dried pressure conditions, its subsequent treatment will include or high temperature, high pressure consolidated wood a humidification to increase the moisture content to about fiber sheet by markedly quicker means than heretofore. I 7% to 13% of the board weight. If the board is con- In the manufacture of wood fiber sheets,such as either solidated into a high density hardhoard, a humidification hardboard or low density panels, tile or sheathing, a wet will follow consolidation to increase the moisture conmat of fibers is first formed, as by felting, land is subsetent to about 5% to 9% of the board weight. quently dried in low density form in dryers by forced It is the above described humidification step with which circulation therein of warm, dry air. Following the drythe present invention is concerned. FIG. 1 shows scheing process, in either the subsequent finishing processes matically, the processof the invention wherein either low or storage, a bone-dry sheet will tend slowly .to take on density wood fiber board from a conventional dryer or moisture from the atmosphere until ,it contains a normal l-gh density WOOd fi hard'board from a on n i al humidity of about 5% to 10% moisture content. If h boa d h p u high pressure consolidating ll d t creme to normal h i i by taking i t platen press, either designated as 10, is rolled between from the atmosphere in this manner, the absorption 1; submerged press rolls 12in accordance with the invention,

the moisture proceeds very slowly and unevenly. Deand subsequently surface dried at 14, to remove excess creasing drier time to stop the drying process when nornon-absorbed water, p g finished llhiformlY mal humidity is reached is undesirable since the moisture midified P I I in the sheet at such time is very unevenly distributed there In 511% humidification of l n y Wood fiber ar throughout and further, it is very ditficult to control the board subsequent y having a moisture @011- drying time to obtain a desired moisture content. t -h om i Pl d nd r Wat r 22, and

In the subsequent use of low density wood fiber prodrolled between rolls 26 Which sp ucts, such as sheathing, it is preferable that the product that h board for Substantial distance -6 ghave slightly more moisture content than equilibrium, ihg from heheath t T0118, rhm'ahls Submerged in vthe since a shrinkage resulting from a slight subsequent dry- Water Thl's is p v hyiroiaiahly'disposihg a lower ing after application to building studs is of no substantial T011 4 pl Submerged in a (Bank Of Water 22 d harm, whereas an expansion and bulging due to a further y mounting an Upp r011 26 directly 'thefeovel absorption of moisture after application to building studs 40 with at'leaht P t f roll 26 disposed Within h Water is a definitely undesirable condition. 22.

Alternatively, if the low density sheet is to be used in The F0116 26 are 10 Provide an evenly the a uf tur f h b rapid, hi h even hm tribu-ted load across the board width as the board passes midificatron of the board immediately following the high "through the hip between thevrolls. s d l ed to temperature, high pressure consolidation to the high denbe varied With 3 diameter of rolls Me of vh'avfil sity condition, is even more essential and critical, since thlhllgh T0115 24, Variation in the density 0f the hoard, otherwise a problem of wara is d the resiliency of the board, water temperature and the controlled humidification of the dried wood fiber sheets, such as by elaborate vapor chambers subjecting all suran amount Whlch would Crush Otherwlse damage faces evenly to the water vapors. The cost of such equipboard in other Words, never excfied the elastic limit, ment and the time required for such an operation, howa lesser Mad may be used with plurality of Passes of ever, is unduly high. the board to obtain the highest degree of humidification.

It is a principal object of the present invention to pro- A normal degTee humidification desired in low density vide a method of susbtantially instantaneously increasing Wood fiber board is from about 8% to 13% moisture, and the moisture content of the wood fiber sheet product with a 300 Pound P lineal inch load TOMS Z4, of six uniform distribution of the moisture throughout the wood inCh diameter has been found o provide a highly' unifib Sheet product. form humidification within this range with low density It is a f th r Object f the invenfion provide Such board of about 0.4 specific gravity, water temperature of method with a mquirement only of relatively inexpensive 150 F., rate of. travel through rolls of about 100 feet per control. the diameter of rolls 24, 26, the higher the load must be These and other objects of the invention will be more to fi 9 ff the necessary pressure on board In readily apparent when considered in relation to the preera the Otter the Water lower the reqmred pres" 5 i i fgrred embodiment as set forth 1n the specification and 6 f igfif ff gzhg fi higi 212 5 11? aga iilizr iiai s own in the drawings in which: i k FIG. 1 is a schematic diagram of the method of the boarq having a speclfic lgtavlty of Over Subsequent to present invention. 1 carried out in essentiall r i y the manner above described for FIG. 2 1s a side sectional View of the WOOd fi er Sheet humidification of low density board, with the exception obvious lesser compressibility of hardtion. board, roll loads of about two to five times as great as for disposed between said press rolls and while submerged in water to a uniform thickness less than the said normal thickness of said sheet, not substantially exceeding the elastic limit thereof, maintaining substantially uniform pressure of said rolls on said sheet throughout the passage of the entire extent of said sheet between said rolls, and

maintaining all respective portions of said sheet fully submanner in which the exceptionally uniform humidificamerged in water for substantially uniform periods of tion of the method of the invention occurs. After being time immediately following the removal of said portions compressed between the nip of the rolls 24, 26 and emergfrom between said rolls.

'ing therefrom, the board 20 substantially immediately 3. The method of claim 2 wherein said sheet has a springs back to substantially the original thickness, while normal, dry specific gravity of about .4 and wherein said totally submerged in water. This re-exp ansion in ac-- pressure of said rolls on said sheet is about 300 pounds cordance with the invention, has been found to cause an per lineal inch and said rolls have a diameter of about six unusually even distribution of the water throughout the inches.

total extent of the sheet, markedly superior tot rior meth- 4. The method of claim 2 wherein said sheet has a ods, which prior methods also involved substantially normal, dry specific gravity of over 1.0 and wherein said greater processing time. This distribution of the water pressure of said rolls is about 600 to 1500 pounds per is sufilciently uniform such that, by a subsequent slight lineal inch and said rolls have a diameter of about siX amount of capillary action within the board, any final furinches.

ther distribution occurs as necessary to provide complete 5. The method of claim 2 wherein said sheet has a uniformity of humidification. normal, dry specific gravity of about .4, the pressure of Having completed a detailed disclosure of the presaid press rolls on said sheet is about 300 pounds per ferred embodiments of my invention so that those skilled lineal inch, the diameter of said press rolls is about sir in the art may practice the same, I contemplate that variainches, the temperature of said water is about 150 F., tions may be made without departing from the essence and the rate of travel through said rolls is about 100 of the invention or the scope of the appended claims. feet per minute.

I claim: 6. The method of claim 2 wherein said sheet has a l. The method of increasing, under controlled condinormal, dry specific gravity of over 1.0, the pressure of tions, the moisture content of a substantiallydry manusaid press rolls on sai sheet is about 600 to 15 00 pounds factored wood fiber sheet comprising the steps of roll per lineal inch, the diameter of said press rolls is about pressing a substantially dry manufactured wood fiber six inches, the temperature of said water is about 150 sheet while submer ed in water and under pressure suffi- F., and the rate of travel through said rolls is about 100 D cient to lessen the thickness thereof not substantially exfeet per minute.

References Cited in the file of this patent ceeding theelastic limit thereof, and maintaining the said sheet submerged in water immediately after removal from said roll pressing for a period of time suflicient to permit UNITED STATES PATENTS suction of water into the interstices of said sheet. M J 1 2 19,24 2. The method of uniformly humidifying \a substan-- E y 2 v tially dry manufactured Wood fiber sheet comprising the 40 Sse an 1934 OTHER REFERENCES 1 Quotation from page 141, Scientific American, Aug. 26, 1893.

low density board have been found necessary to provide H the rapid uniform humidification to the normal degree of about 5% to 9% moisture desired for hardboard. On very incompressible hardboards, multiple sets of pressure rolls 24, 26 may be desired, especially at high speeds, to 5 attain the desired humidification. r

The fragmentary sectionalview of FIG. 3 shows the steps of passing a susbtantially dry manufactured wood fiber sheet of substantially uniform normal thickness and density therethroughout, between a pair of opposed rotatable press rolls, compressing the portion of said sheet 7-"... Pee-rants, i i 

1. THE METHOD OF INCREASING, UNDER CONTROLLED CONDITIONS, THE MOISTURE CONTENT OF A SUBSTANTIALLY DRY MANUFACTURED WOOD FIBER SHEET COMPRISING THE STEPS OF ROLL PRESSING A SUBSTANTIALLY DRY MANUFACTURED WOOD FIBER SHEET WHILE SUBMERGED UN WATER AND UNDER PRESSURE SUFFICIENT TO LESSEN THE THICKNESS THEREOF NOT SUBSTANTIALLY EXCEEDING THE ELASTIC LIMIT THEREOF, AND MAINTAINING THE SAID SHEET SUBMERGED IN WATER IMMEDIATELY AFTER REMOVAL FROM SAID ROLL PRESSING FOR A PERIOD OF TIME SUFFICIENT TO PERMIT SUCTION OF WATER INTO THE INTERSTICES OF SAID SHEET. 